Table 4.

Performance of Xpert Against the Reference Standard of MTBDRplus (Line Probe Assay) for Multidrug>-resistant Tuberculosis Detection

Xpert RIF Resistant	Total	MDR-TB by LPA
		Positive	Negative
Results
Positive	73	45 (a)	28 (b)
Negative	90	0 (c)	90 (d)a
Total	163	45	118
Sensitivity, % (95% CI)	…	100.0 (92.1–100)
Specificity, % (95% CI)	…	76.3 (71.2–85.6)
Positive-predictive value, % (95% CI)	…	61.6 (49.5–72.8)
Negative-predictive value, % (95% CI)	…	100.0 (96.6–100)

Sensitivity = a/a + c; Specificity = d/b + d; positive-predictive value = a/a + b; negative-predictive value = d/d + c.

aThe 2 invalid isoniazid results by LPA were assumed to be susceptible (ie, did not detect MDR-TB) and included in the denominator for the calculation of specificity.

Abbreviations: CI, confidence interval; LPA, line probe assay; MDR-TB, multidrug-resistant tuberculosis; RIF, rifampicin.